Compound master cylinder



Sept. 7, 1943. .s. ScHNEI-L 2,328,683

COMPOUND MASTER CYLINDER Filed Sept. 26, 1941 mm 4Q INVENTOR STEVE SCHNE LL Patented Sept. 7, i943 Steve.Schnell, Kirkwood, Mo ammo a. wit net Electric Corporation, St. Louis, Mo., a corporationolllelaware. v Application September 26, 1941, Serial o. 412,468 ccmims'wiico-sae) H My invention relates to master. cylinder del3 tothus place'thejinterior of the cylindrical exvices' for fluid pressure actuated systems and tension 1 in constant communication with the.

more particularly to a compound master cylininterior of the reservoir casing. der whereby the pressure created may be in- The flange 4 is formed with one or more slots creased without proportionally greater increase 5 ll which permit the reservoir to communicate in the applied operating force. 7 K with the outlet 3 and with the interior of cylin- One of the objects of my invention is to proder 9 through the cylindrical extensionv l2 andvide an improved compound master cylinder 1 an opening l8 in wall Ii when the cylinder 9 is wherein the transition from the low pressure proin its rearmost position shown. Positioned in ducing means to the high pressure producing 10 the annular space between flange and extension means maybe effected in a smooth manner. 5 of plug 2 is a sealing member l9of rubber Another object of my invention is to produce or like material having an annular ridge 20 for a compound master cylinder wherein efli cient wooperation with the end surface 2i on extension compensation between the pressure producing l2. It is thus seenthat when cylinder 9 is moved system and the reservoir is permitted without forwardly, slot il will be closed and the sealing employing compensating portholes which must member I9 will .be engaged and compressed to be passed by the sealing cups. thereby prevent any communication between cyl- Among other objects of my invention is to proinder 9 or outlet 3 and the reservoir.

duce a compound master'cylinder which can be Positioned within cylinder 9 for reciprocation economically manufactured and which will be is a Piston 22 having a Sealing D The D simple in construction and efficient in operation. ton is threaded to the inner end of a plunger 24 Still other objects will become apparent from passing through the cylindrical extension 1 and the following description taken in connection therear wall l3 of cylinder 9. A piston rod 25 with the accompanying drawing in which the is connected to the rear end of the plunger for single figure is a sectional view of a compound 25 reciprocating it and piston 22. A sealing cup master cylinder embodying my invention and 26 seals the rear end of the plunger and the exshowing the parts in their inoperative positions. tension 'I and a dust boot 2'! is provided between Referring to the single figure in detail, I indithe piston rod and the end of the extension. A cates a reservoir casing provided with a threadsealing cup 28 is also carried in a groove 29 at ed plug 2 at its forward end and having an out- 30 the rear end of cylinder. 9 adjacent wall l3 for let passage 3 therein to which is connected the preventing fluid from escaping past the wall and usual conduit leading to the fluid motor or other plunger from chamber 30 at the rear of piston 22. device to be actuated by fluid pressure. The The plunger is provided with communicating inner end of the plug is provided with a cylinstepped bores 3| and 32 at the juncture of which drical flange 4 and a central projection 5 through 35 is a valve seat 33. The bore 3! communicates Y which the outlet passage extends. At the rear with cylinder 9 ahead of piston 22 by an openend of the casing there is also provided a threading 34 (smaller than the diameter of bore 3!) ed member 6 havinga cylindrical extension I through the piston and with chamber 30 by a and an annular flange 8 extending into the inpassage 35. Within the bore is a valve element terior of the casing. 36 carried by a valve rod 31 and cooperating with Within the reservoir casing is positioned a the piston 22 to control passage 34. The rear cylinder 9 mounted for limited reciprocable of the valve rod carries a second valve element movement. Theforward end of this cylinder has 38 for cooperation with the valve seat 33 and asthreaded thereon a member Illv forming an end sociated with this valve element is a cup 39 for wall II for th cylinder. The member In is pro- .45 preventing fluid from flowing from bore 3| to vided with a cylindrical extension l2 of smaller bore 32 but capable of collapsing sufliciently that diameter than cylinder 9 which is slidably refluid can flow in the opposite direction. A spring ceived in flange l of the forward plug 2 to thus 40 in bore 32 normally biases the valve rod so constitute a support for the front end of cylinrthat valve element 36 closes opening and valve der 9. The rear end of the cylinder is provided element 38 is unseated. A passage ll constantwith an inwardly extending end wall I3 and an I 1! pla es bore 32 in c munic ion wit the annular flange llfor receiving the flange 8 on cylindrical extension I and the rv l y Way the member 8 to thus'constitutega support for of slotsl5 and I6.

the rear end of the cylinder. The flange i4 is The friction between sealing cup 23 and cylin-.

provided with slots l5 and flange 8 with slots der 9 and the friction between sealing cup 28 surface 2| voir in the event the piston should be moved quickly and thus have some relative movement with respect to the cylinder before the valve means atthe forwardend is closed, there is provided a washer 42 ofslightly less diameter than the internal diameter of the cylindrical exten sion l2. A weak spring 43 maintains this washer in engagement with the end of projection 5. Thus it is seen that the washer restricts flow from cylinder 9 to the reservoir when the valve means is open. Fluid may flow from the reservoir to'cylinder 9 without appreciable restriction as the washer can be moved away from the end of the projection by compressing weak spring 43, Referring to the operation of the master cyl-. inder device, the parts will be in the positions shown in the figure when the master cylinder is inoperative. Under these conditions the reservoir will be filled with fluid as will also the cylinder 9 ahead of piston 22 and chamber 39. The

bore 32 will also be fllled with fluid since it is in constant communication with the reservoir. The cylinder 9, as well as the outlet passage, will be in communication with the reservoir to thus permit compensation for any expansion and contraction of the fluid since the Surface 2| on the extension l2 will be disengaged from the sealing member l9 and slot ll uncovered. It is also to be noted that in the inoperative position of the master cylinder, the valve element 36 closes the opening 34 and the valve element 38 is off the valve seat 33. If the fluid in chamber 39 contracts, additional fluid can flow thereto from the reservoir by passing sealing cup 39. Any expansion of the fluid in chamber 30 vn'll be compensated for by the opening of the valve element 36 by the pressure of the fluid in chamber 39 acting on cup 39. It is to be noted that the crosssectional area of cup 39 is considerably greater than the cross-sectional area of valve element 36 which is subject to fluid pressure tending to hold it closed.

When the piston rod 25 is moved to the left to operate the master cylinder, piston 22 and plunger 24 are simultaneously moved forwardly therewith. The friction between the cup 23 and the cylinder wall and the friction between cup 29 and the plunger will also cause cylinder 9 to move forwardly with piston 22 and the plunger until the surface 2| on extension l2 engages the ridge 29 of the sealing member l9. voir will'now be cut off from communication with the portion of cylinder 9*ahead of piston 22 and also with the outlet passage 3. As piston 22 is caused to continue to move forwardly, it will have relative. movement. with cylinder 9 and pressure will be developed in cylinder 9 whereby fluid under pressure will be forced out of the outlet passage to operate the fluid motors which are connected by a suitable conduit with said outlet passage. As soon as pressure is developed in cylinder 9 ahead of piston 22, it will act upon the wall H and produce a force tending to hold in engagement with the sealing member l9. The sealing member l9 will not be excessively compressed, due tov the engagement of member l9 with the'flange 4. This force will increase as the pressure in cylinder 9 increases asaaosa and, therefore, surface 2| will be held agains the sealing member under all conditions.

If the'piston rod 25 should happen to be moved quickly from its inoperative position shown in the figure, the inertia of the cylinder may result in piston 22 having relative movement with the cylinder before surface 2| on extension |2 engages the sealing member l9 to cut oil communication with the reservoir. This relative movement, however, will be very slight since as the piston moves relatively to the cylinder, pressure will be immediately developed in the portion of the cylinder ahead of the piston due to the fact that washer 42 will restrict flow of fluid to the reservoir. The pressure developed in cylinder 9 ahead of the piston will act upon the end wall and immediately cause the cylinder to move forwardly so that the surface 2| will engage the sealing member 9 to cut off communication with the reservoir.

As piston 22 moves forwardly after communication with the reservoir is cut off and fluid pressure is being developed, chamber 39 at the rear of piston 22 willincrease in volume and a sub-atmospheric pressure will be developed. This will result in fluid flowing from the bore 32 in the plunger past the open valve element 38 and the periphery of the sealing element 39 and into the chamber 39. It is thus seen that this chamber, although increasing in volume, will continue to be filled with fluid.

When the pressure being developed by piston 22 reaches a predetermined value which will be determined by the strength of spring 49 and the The reser- L P seat 33.

. area of opening 34, valve element 36 will be forced off its seat to thus place the portion of the cylinder ahead of piston 22 in communication with chamber 39. The pressures-of the fluid in the cylinder and chamber 39 will now be equalized. The pressure in chamber 39 will now be effective on the sealing cup 39 and the sealing cup and valve element 38 will be quickly forced rearwardly against the action of spring 49 so as to cause the valve element 38 to become seated on Due to the larger cross-sectional area of cup 39, the pressure in chamber 39 will now maintain valve element 36 unseated and also prevent it from fluttering. The pressure in chamber 39 will continue to maintain the valve element 38 seated so that valve element 36 will be held unseated.

With the valve element 36 held open, continued movement of the piston rod 25 will now result in plunger 24 developing pressure in the cylinder. Pressure will no longer be developed by piston 22 since fluid can flow past the piston. Since plunger 24 has a cross-sectional areaeflfective to develop pressure which is less than the crosssectional area of piston 22, continued movement of the piston rod will develop pressure at a higher ratio. With a, smaller area becoming eifective to developpressure, less manual force will be necessary to increase the fluid pressure being developed than would b the case if the piston 22 continued to develop the pressure alone.

When the pressure is being developed by plunger 24, the fluid pressure in chamber 39 will be effective on the rear wall |3 of the cylinder. However, since the area of this wall is much less than the area of the forward wall there'will continue to be a resultant force tending to hold the surface 2| on extension |2 engaged with the sealing member l9.

When it is desired to release the developed pressure, piston rod 25 is permitted to be retract- ,veloped pressure. The valve 36 will remain open I and the valve means at the forward end oi. cylinder 9 willremain closed. When piston 22 reaches its retracted position atrthe rear end of i the cylinder, th fluid pressure in cylinder 9 acting on piston 22 will cause the cylinder to move rearwardly and disengage the surface 2| fromthe sealing member l9, thereby opening slot I! so that the pressure can be relieved and any excess fluid flow into the reservoir. The movement of the. cylinder 9 rearwardly to open the valve means at the forward end of the cylinder is brought about by a diflerential force acting on cylinder ,9 through piston 22 which, it is noted, is engaged with a shoulder atthe rear end of the cylinder. As soon asthe valve means at the forward end of the cylinder is 'opened to relieve pressure in the cylinder, the valve means .96 will be closed under the action of the spring 49. The parts will then again be in'their normally inoperativ positions as shown inthe flgure. The cylinder 9, as previously stated, will not be moved rearwardly to open the valve means at the forward end of the cylinder untilpiston 22 reaches its retracted. position. This is true as long as there is fluid pressure in the cylinder during the retracting movementofpiston '22. and plunger 24, conditions which normally prevail. However, if piston 22 should be returned at a more rapid rate than fluid is returnedthrough the outlet passage (due to the pull of a spring on the brake pedal or a restriction in a fluid line) the fluid pressure in cylinder 9 will drop below atmospheric pressure. Then under such conditions cylinder 9 willbe pulled rearwardly by the friction of the cup 23, thus opening the valve means at the forward end of the cylinder and permitting fluid to flow from the reservoir. These conditions, however, will not normally be present as the fluid under pressure will usually be returned from the motors faster than the re-. turn movement of the piston 22, thus insuring that fluid under pressure will be maintained in cylinder 9 until the piston and plunger reach 3 Fluid trapped in chamber 30 will open valve 29 and pass piston 22 during its return movement.

It is to be noted from the structure described that there is not present any compensating ports which are uncovered by a sealing cup when a: piston is returned to its retracted position as is the usual present practice. B eliminating the compensating port, the life of the sealing cup is greatly increased since it will not be out by the pcrthole. Consequently, the etjtlciency of the cup is greatly increased. Although the compensat-' ing ports have been eliminated, interchange of fluid between the reservoir and cylinder is nevertheless permitted to compensate for contraction and expansion of the fluid when the master cylinder is inoperative. Also, by means of the construction described the change-over from the low pressure producing means to the high pressure producing means will b smooth and without shock to the operator.

Being aware of the possibility of modifications in the particular structure herein described without departing from the fundamental principles of my invention, I do not intend that its scope be limited except as set forth by theappended claims.

Having, fully described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. In fluid pressure apparatus, a support, a cylinder mounted on the support for limited reciprocable movement, means forming an outlet passage for the cylinder, a piston in said cylinder, a reservoir, means comprising valve means associated with the outlet passage and controlled by the reciprocable movement of the cylinder for controlling communication between the reservoir I and both. the cylinder and the outlet passage,

means for moving the cylinder forward to close the valve means when the piston is moved ior- .ward, a second piston or smaller cross-sectional their retracted positions. If any fluid should be trapped in chamber 30, due to theclosing of the valve 36 as a result of a rapid fall in pressure in" cylinder 9, the continued return movement of piston 22 will result in pressure again rising in chamber 30 and thus again opening the valve so as to relieve this pressure.

If it is desired to relieve only part of the pres sure developed then-,the piston rodneed only be partially retracted. Since normally the valve means atthe forward end of cylinder 9 remains.

closed until thepiston reaches its retracted posiarea than the first piston, means for connecting the pistons together for simultaneous movement at all times, means for moving the pistons,

and means comprising valve means carried by the pistons and automatically operative upon the development of a predetermined pressure by the first piston for rendering said first piston ineffective. to develop pressure 'andpermitting additional pressureto be developed by the second piston.

2. In a fluid power transmitting system comprising a conduit for supplying fluid under pressure '"and a fluid reservoir, a fluid pressure producing device comprising a reciprocable cylinder and a reciprocable piston therein having a fluid outlet port in communication with the fluid supplyconduit and said fluid supply conduit and movement of piston 22. When the piston is-initially retracted the friction of the cup will pull the cylinder rearwardly and open the valve means .to permit fluid to: flow from the reservoir been forced out through a valve in the system. which has been opened .to permit the bleeding.

. into the cylinder to replace the fluid which has cylinder port being normally in communication with the fluid reservoir, valve mean controlled by the reciprocable movement of the cylinder, means functioning when the piston moves forwardly for moving the cylinder forwardly to close the valve means and thereby prevent flow of fluid to the reservoir, said means permitting relative movementbetween the piston and the cylinder after the valve means is closed, means comprising valve means carried by the piston for automatically'rendering said piston inoperative upon the creation of a predetermined pressure in the cylinder ahead of the piston and for placing the portion of the cylinder at the rear of the piston in communication with theoutlet, means for continuing to apply pressure to the fluid after said piston becomes inoperative and comprising a second piston having a smaller effective cross-sectional area than the first piston,

controllingcommunication between the reservoir and the cylinder, means for developing alow pressure and comprising a piston reciprocable in said cylinder, means forclosing said valve means by a movement of the cylinder when the piston is moved,forwardly, other valve means carried by the piston and operable upon the development of a predetermined pressure ahead of said piston for placing the chamber at the rear of the piston in communication with the portion of the cylinder ahead of the piston, and means comprising a plunger at the rear of the first named piston for developing a high fluid pressure when said last named valve means is opened, said plunger being smallerthan the'cylinder and extending through the rear wall thereof, packing means for the plunger carried by the rear wall of the cylinder, and means for moving-said piston and plunger simultaneously in a pressure producing direction.

4. In fluid pressure producing apparatus, a cylinder having a rear wall, an outlet for the cylinder, a piston reciprocable in said cylinder, a plunger secured to said piston for simultaneous movement therewith and extending rearwardly thereof through the rear wallof the cylinder, said plunger being of smaller diameter than the piston and cylinder, packing means for the plunger so positioned at the rear end of the cylinder as to permit the plunger to have relative movement thereto, means comprising a valv element carried by the piston for automatically rendering said piston inoperative upon the creation of a predetermined pressure in the cylinder ahead of the piston and for placing th portion -of the cylinder at the rear of the piston in communication with the outlet, means for reciprocating the piston and plunger, valve means for permitting fluid to fiow to the space at the rear of the piston when said piston is developing pressure, and means for closing the last named valve means by a movement of the valve element to its open position.

5. In fluid pressure producing apparatus, a

reservoir, a cylinder reciprocabl therein, an outlet for the cylinder, valve means controlled by the reciprocation of the cylinder for controlling communication between the reservoir and both the outlet and the cylinder, said valve means when closed permitting the cylinder to be in communication only with the outlet, a piston in the cylinder, a chamber at the rear of the piston, a second piston of smaller diameter than the first secured to said first piston and capable of applying pressure to fluid in the chamber, a conduit through the first piston for placing the chamber at the rear thereof in communication with thecylinder ahead of the piston, valve meansthe cylinder forwardly with the pistons tothereby close the first named valve mean when said pistonsare initially moved from their inoperative positions.

6. Infiuid pressure producing apparatus, a

reservoir, a cylinder reciprocable therein, an outlet for the cylinder, valve means controlled by th'e reciprocation of the cylinder for controlling communication between the reservoir and both the outlet and the cylinder, said valve means when closed permitting th cylinder to be in com munication with the outlet only, a piston in the cylinder, a chamber at the rear of the piston, a second piston at the rear of the first piston and reciprocable with the first piston to apply pressure to fluid in the chamber, said pistons being of different diameters, a conduit through the first piston forplacing the cylinder thereahead in communication with the chamber, valve means for controlling the conduit, means for reciprocating the pistons, means for moving the cylinder forwardly with the piston to thereby close the first named valve means when said pistonsare initially moved from their inoperative positions, and means comprising valv means carried by the second piston for permitting'fiuid to ,fiow from the reservoir into th chamber at the rear of the first piston during the time said first piston is efiective to develop pressure. I STEVE SCHN'ELL. 

